(1) Field of the Invention
The present invention relates to a tractor transmission including a plurality of change speed gear mechanisms, and to a tractor equipped with such a transmission.
(2) Description of the Prior Art
A known tractor transmission including a plurality of change speed gear mechanisms is disclosed, for example, in U.S. Pat. No. 4,628,768. As exemplified by this disclosure, the known transmission invariably includes clutch means, a backward and forward drive switching mechanism, a main change speed gear mechanism, and an auxiliary change speed gear mechanism interconnected in series longitudinally of the tractor. There is a limit to reduction in longitudinal dimensions of such a transmission by reason of its structural conditions. A proposal has been made as disclosed in U.S. Pat. No. 4,513,834, to reduce the longitudinal dimensions of the transmission. According to this proposal, an engine drive is input to a hydraulic stepless change speed mechanism through clutch means, and an output of the hydraulic stepless change speed mechanism is transmitted to the rear wheels through a vertical reduction mechanism. The stepless change speed mechanism may reduce the longitudinal dimensions of the transmission but requires a considerable space in the vertical direction. Furthermore, it is only in limited cases from the point of view of transmission efficiency and cost that the stepless change speed mechanism is employed in favor of a gear type change speed mechanism.